Synergistic mechanisms of mechanochemical activation on the mild oxidative desulfurization of superfine pulverized coal

Abstract

Abstract Exploiting efficient and low-cost oxidative desulfurization methods is urgently needed for promoting the development of novel desulfurization technologies. In this work, the sulfur speciation in the mechanochemically activated and H2O2 oxidized coals was quantitatively characterized through X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). The influences of H2O2 concentration and particle size on the sulfur transformation were discussed. In addition, the synergistic mechanisms of mechanochemical activation and H2O2 oxidation on the removal of organic sulfur were focused. Finally, combined with the sulfur speciation and deconvolution analysis, the main SO2 precursors during the pyrolysis were elucidated. The results indicate that mechanochemical activation can promote the conversion from organic to inorganic sulfur by reducing the strength of C-S bond and accelerating the oxidation of thiophene and sulfide, which is beneficial to remove organic sulfur. On the other hand, the dissolution amount of sulfate in small particles decreases due to the decreased macropore volumes, complicated pore structure, and increased mass transfer resistance. Then, an optimal particle size around 20\xa0μm (i.e., HN_23.9 and NMG_18.7) is observed for the studied coals, where the reduced amplitude of SO2 after the chemical oxidation reaches the maximum. Besides, a dilute oxidant concentration is needed for low-rank coal during the chemical removal of sulfur, which is conducive to reduce the cost. The findings shed light on elucidating the origination of sulfur oxides from a molecular level and further exploiting the new efficient and low-cost desulfurization technologies.